Catheter tip assembly

ABSTRACT

A catheter having an improved tip structure. The catheter tube has a relatively low durometer tubular body portion and a separate higher durometer molded tip thereon which does not collapse when it strikes an obstruction during insertion. Preferably, the tip assembly is precision molded from a suitable plastic, such as PVC, acrylates, urethanes, styrenes or the like, having a durometer greater than the tube body, and an inwardly tapering contour to provide for ease of insertion. The distal aperture of tips for endotrachael-type tubes also have nonbeaded, chamfered leading edges. The tips may be color coded to the internal diameter of the catheter tube for easy operating room identification, and may be radio-opaque. The tube body is precurved into a hyperbolic shape with the distal end being the &#39;&#39;&#39;&#39;straight&#39;&#39;&#39;&#39; part of the hyperbolic curve, terminating in the molded tip.

Bazell et a1.

[ June 24, 1975 CATHETER TIP ASSEMBLY Assignee:

Filed:

Appl. No.: 434,937

Inventors: Seymour Bazell, Skokie; Ralph G.

Ostensen, Morton Grove; Edward M. Goldberg, Glencoe, all of 111.

Medical Products Corporation, Skokie, 111.

Jan. 21, 1974 Related US. Application Data Division of Ser. No. 301,172,Oct. 26, 1972.

US. Cl 128/351; 128/239 Int. Cl A6lm 25/00 Field of Search 128/239,348-351 References Cited UNITED STATES PATENTS 10/1883 Mayall 128/23911/1966 Clark 12/1970 Birtwell 128/349 B 12/1971 Sheridan 128/349 B3/1973 Vaillancourt et a1. 128/349 R X 5/1973 Walker et a1. 128/3513,788,327 l/1974 Donowitz et a] 128/350 R Primary Examiner-Dalton L.Truluck Attorney, Agent, or F irmMolinare, Allegretti, Newitt & Witcoff[57] ABSTRACT A catheter having an improved tip structure. The cathetertube has a relatively low durometer tubular body portion and a separatehigher durometer molded tip thereon which does not collapse when itstrikes an obstruction during insertion. Preferably, the tip assembly isprecision molded from a suitable plastic. such as PVC, acrylates,urethanes, styrenes or the like, having a durometer greater than thetube body, and an inwardly tapering contour to provide for ease ofinsertion. The distal aperture of tips for endotrachael-type tubes alsohave non-beaded, chamfered leading edges. The tips may be color coded tothe internal diameter of the catheter tube for easy operating roomidentification, and may be radio-opaque. The tube body is precurved intoa hyperbolic shape with the distal end being the straight part of thehyperbolic curve, terminating in the molded tip.

4 Claims, 12 Drawing Figures PATENTEIJJUN24 I975 I 3.890.976

SHEET 2 SHA PE 4 1 CATHETER TIP ASSEMBLY CROSS-REFERENCE TO RELATEDAPPLICATION This application is a divisional of our co-pendingapplication Ser. No. 301.172, filed Oct. 26, 1972.

FIELD OF THE INVENTION This invention relates to catheter tubes usefulin medical situations, such as endotracheal tubes, tracheostomy tubes,Foley catheters and the like, where a tube is inserted into the body formedical reasons. More particularly, the invention relates to improvedcuff and catheter tip assemblies, methods of construction andretrofitting of the cuffs to the tubes. Most specifically, the inventionrelates to providing a special silicone rubber cuff which may beemployed with dissimilar plastic, rubber, or metal tubes to which thesilicone rubber is normally nonbondable to provide a cuff which producestransmural pressures upon sealing inflation of values which tend not toinduce substantial tissue pressure necrosis. The .tip assembly isprecision molded of a plastic. rubber, or silicone rubber material ofequal or higher durometer than is used for the body portion of the tubeitself, and is characterized by a tapered profile to reduce tissuelesions upon insertion or removal, and precision molded chamfered edgesand openings. The tip may also have a medially extending tapered collaror bevel for fitting or sealing the tip to the body portion of the tube.

BACKGROUND OF THE INVENTION Catheters are extremely important and usefulmedical tools for the input or withdrawal of fluids from the body of apatient. Generically, catheters are tubular in shape and have aretaining and/or sealing inflatable balloon cuff near the distal(intracorporeal) end of the tube. Often the catheters must remain inplace for substantial periods of time. Present catheters have not beenentirely satisfactory since they tend to cause tissue necrosis frompressure or biochemical incompatibility of the inflatable balloon cuffs.For example, standard rubber cuffs of endotracheal tubes in place for aslittle as 72 hours can cause severe necrosis. Latex material ischemically irritating, and polyvinylchloride plastic cannot elongatesufficiently to provide adequate low pressure balloon volumes, has nomemory and prunes upon deflation.

Physicians and anesthesiologists are only just now becoming aware of thesevere damage which catheter tubes may cause at the time of insertion orwithdrawal from the body and of the damage which inflated cuffs maycause on the adjacent tissues with which they come into contact.

In early tubes of rubber material construction, for example theRusch-type tubes, the tube, tip, and inflatable cuff were made ofuniform durometer material. However, the durometer had to be selected tobe sufflciently hard for ease of insertion into the body. When the tubeis too soft, insertion of an endotracheal tube (taken by way ofillustration) becomes exceedingly difficult since the tube tip maycollapse or the tube may kink upon being forced past the vocal chords.

With the advent of newer plastic materials such as polyvinylchloride(PVC), attempts were made to provide all-PVC tubes, i.e. tube, cuff andtip of PVC. Although the PVC was well suited to make the body of thetube, PVC cuffs were not suitable because the PVC is of lowextensibility. The PVC cuffs are extremely hard and transmit pressuressufficient to cause venous collapse in the surrounding tissues. Thisvenous collapse is then followed by buildup of edema which in turnresults in back pressure sufficient to cause capillary collapse. Thevascular beds adjacent to the site of contact of such cuffs becomesufficiently constricted in normal use that pressure necrosis andischemia occur causing medically significant damage to the tissues. Thisis well documented in the literature.

One approach to attempting to solve the problem was to providenonextensible. large residual volume (oversized) cuff constructions.These oversized cuffs were characterized by having the PVC plastic,latex, or rubber in an enlarged, baggy or folded condition prior toinsertion. It was postulated that relatively high volumes of intra-cuffair would be required to expand those loosely folded cuffs into contactwith the trachea walls,

as in the case of endotracheal or tracheostomy tubes. However, there wasno full recognition of how low the critical pressure had to be; i.e.pressure which could be transmitted safely to the adjacent tissueswithout causing significant tissue pressure necrosis. For example,Cooper et al, in Experimental Production and Prevention of Injury Due toCuffed Tracheal Tubes, Surg., Gyn. & Obst., December 1969, p. 1235-1241,considered that intramural pressures on the order of 40 mm. of mercurywould be permissible. However, these pressures are far too high.Efferent venous collapse occurs at a range of 4-7 mm. mercury; in thesupine individual (e;g. during surgery) venous collapse occurs atpressures from about 8-15 mm. mercury, with the average being aboveabout 10 mm. mercury. The capillary bed constriction commences atapproximately 20-25 mm. mercury.

However, typical prior art material such as rubber and polyvinylchlorideproduce transtracheal or transmural pressures, measured by thedifference between the pressure at seal and the contact pressure, offrom about 29-210 mm. mercury. This is from to 1050 percent greater thanthe critical 20 mm. mercury pressure for commencement of capillary bedconstriction.

A further problem with the oversized tube of cuffs is that the insertionprocedure is blind, i.e. the anesthesiologist is unable to view thevocal chords upon insertion of the tube. Consequently, the vocal chordscan be damaged upon insertion. As a natural reaction to this, theanesthesiologist usually picks a tube which is quite small relative tothe size of the trachea. However, this defeats the purpose of theoversized cuffs, since upon inflation, the cuffs are not extensible anddo not have the slack with which they were designed to permit low volumeinflation. In order to make full seal, additional air volume must beapplied. But the pressures transmitted by the cuff to the trachea wallsthen exceeds the critical pressure of vascular constriction.

If proper sized tracheal tubes are used with the oversized cuffs, thecuffs upon inflation have wrinkles and folds in them which may promoteleakage and imperfect seal. In order to compensate for this, theanesthesiologist in actual operation tends to overinflate the cuff inorder to flatten the wrinkles against the inside of the trachea tube. Inthe process, uneven pressures are developed. More significantly, from amedical view, pressures in excess of critical vascular constrictivepressures are developed.

Because of the inelasticity of PVC. it cannot be used in satisfactorystandard non-oversized type construction form of endotracheal tubes. Buteven in oversized forms, the anesthetist in actual practice attemptsprestretching the very hard PVC plastic film used for the cuff byheating it, for example, by holding it under hot tap water. However,this renders the endotracheal tube non-sterile, and permits the PVC toexpand nonuniformly and take an improper set" when it cools. Neither areconducive to medical safety. Martinez, in Anesthesiology 34, pp. 48889l97l) reports extensive tracheal necrosis associated with a prestretchedtracheostomy tube cuff.

In short, the prior art went in the direction of constructional designchanges (oversized cuffs) in an attemptto overcome the poor propertiesof PVC and rubber then in use, e.g. hardness and inelasticity. But in sodoing, they were insensitive to the actual surgical problems that theresulting oversized cuffs presented. These problems led to overinflationwhich is a fullcircle return to the hard inelastic properties of PVC andrubber then in use.

There is still another problem associated with the PVC plasticcatheters. Normally the tube in an endotracheal or trachestomy tube hasan end which is cut on a bias in order to facilitate ease of insertion.The tubes are normally extruded and the insertion ends are biascut andheat treated to smooth the rough-cut ends with RF, infrared, resistanceheating or flame. However, the heat treating of the tip of the plasticPVC tube causes a bead-like thickening at the edge. This tends to makethe outside diameter of the tip larger than the nominal diameter of thetube, and at the same time renders the internal opening in the tube ofsmaller diameter than the nominal diameter of the tube. The former meansthat the tube is larger and tends to cause more damage upon insertion.The latter means that tubes passed down the central lumen of thetracheostomy tube or endotracheal tube, e.g. drainage tubes or the like,must be smaller than maximum capacity in order to pass through theconstricted opening at the tip. Still further, there is no completelyconsistent way of production line control of heat treatment for eachtube. That is, the heat treatment results in each tube having a somewhatdifferent confirmation and degree of enlargement. Thus, since no twotubes have the same configuration, the anesthetist or doctor using thetube may not rely on past experience in making judgments about the sizesof tubes to use in a given medical situation.

Still further, constructing the tube body, from distal to proximal endsof the identical material evidences a failure to recognize thatdifferent portions of the tube must have different properties because ofdiffering functions. As noted above, the cuff should be ofa type whichdoes not have necrosis inducing pressures in the adjacent tissues. Wehave also recognized that the main body of the tube should be relativelyflexible, ofa moderate durometer to be easily bent to conform to naturalvariations in the longitudinal (axial) shape of the trachea or otheropening or passage through which the tube is being inserted. However, wehave discovered that the tip must be of a durometer equal to or higherthan the body so as to provide for ease of insertion and prevent the tipfrom being folded back upon itself upon striking an obstruction. Incontrast, the prior PVC tubes, being heat treated at the end presentsubstantially the same durometer for the tips as for the main bodyportion of the tube. In cases where the heat treatment is excessive, thePVC may actually be degraded and the durometer lowered thus aggravatingthe problem of having too soft a tip.

In our co-pending application, Ser. No. 128,898 we have disclosed andclaimed catheter tubes constructed entirely of silicone rubber having aspecial conformable type cuff of a silicone rubber which has propertieswhich generate transmural pressures that tend not to induce tissuepressure necrosis in the site of cuff inflation. More specifically, wehave therein disclosed our discovery that a silicone rubber of lowmodulus, having properties of a Shore A hardness of less than about 30,a tensile strength of below about 700 psi, an elongation of above about1000 percent, and a stress valueupon sealing inflation of less thanabout 30 percent of the breaking stress of said cuff material permitsproviding flation that do not tend to induce tissue pressure necro-'sis,

However, it has long been impossible, on a practical commercial basis tosealingly bond silicone rubber to polyvinylchloride plastic or to otherplastics, rubber or metal tubes on a consistent. medically reliablebasis. While all-silicone rubber catheters are useful as such, they arerelatively expensive and thus present some hindrance to single use,throw-away application. In addition, many hospitals already havecatheters which employ cuffs that develop pressures too high for medicalsafety.

Therefore, there is a need for a low pressure, low volume, extensible,conformable silicone rubber cuff of special properties which developpressures which are below those which tend to induce any substantialtissue pressure necrosis, and yet may be applied to dissimilar cathetertube body materials, and may be combined with special durometer tips ofprecise, medically noninjurious dimensions, and which may be retrofitonto existing tubes having high pressure, medically injurious I cuffsand/or tips.

SUMMARY One aspect of this invention includes a silicone rubber cuffassembly in which the silicone rubber portion contacting the body tissueinto which the catheter is inserted has special properties such that thetransmural pressure developed by the balloon upon the initial full sealdoes not tend to induce tissue pressure necrosis. A special inner sealsleeve member, or a plurality of seal rings, or bands, of high modulusand durometer silicone rubber are provided and an outer, low modulus anddurometer rubber is bonded thereto. The inner seal member is generallytubular in shape and has a 5-50 percent compression factor, that is, theunassembled diameter of the seal member is 5-50 percent less than thetubular portion of the catheter body on which it is to be mounted. Theinner seal member or rings are stretched over the tube for mounting andthe circumferential tension'the'reof provides a frictional, mechanicaltype of bond to the tube which prevents inflation fluid leakage, andprevents the cuff from being dislodged during use. This permits the cuffto be mounted on tubes of materials which ordinarily do not permitreliable sealing thereto, as by chemical gluing or bonding. Specialprovision is also made for providing a smooth transition between thedistal and proximal ends or margins of the cuff and the catheter tubebody on which it is carried.

The invention also includes a specially molded tip pla'sticequal orharder durometer than standard extruded platic or molded tubes. Thespecial tip is characterized by a tapered profile which assists in caseof insertion. The leading edge of the tip has precision moldedchamferswhich provide for medically smooth traveling edges.

The invention also includes a combination polyvinylchloride tube havingthe cuff assembly of this invention mounted thereon and a speciallymolded selected durometer polyvinylchloride tip secured to the distalend thereof. Such tubes may be constructed having a hyperbolic, curve orset to the tubes with the proximal end being more curved than thedistal, tip and cuff-carrying end. This assists in inserting and lessenstip necrosis in use. This in contrast to the tubes of the prior artwhich naturally carry a semicircular set resulting from manufacturingprocesses employed by PVC tube manufacturers. The tips may be colorcoded to facilitate identification and size mistakes, and may also berendered radio-opaque for fluoroscopic location during use.

THE INVENTION OBJECTS It is therefore an object of this invention toprovide improved cuff and catheter tip assemblies for catheter tubes ofall types.

It is another object of this invention to provide an improved cuff of asilicone rubber material which produ ces transmural pressures atsubstantially full initial seal of values that do not tend to inducesubstantial tissue pressure necrosis at the site of cuff inflation inthe body.

It is another object of this invention to provide a special cathetercuff assembly of silicone rubber material which may be applied todissimilar catheter tube materials, or retrofit on to existing cathetertubes.

It is another object of this invention to provide a special catheter tipof generally equal or harder durometer than used for catheter tubes tofacilitate ease of insertion and withdrawal of the tube in the body andwhich avoids collapsing upon encountering obstructions upon insertion.

It is another object of this invention to provide improved catheter tipswhich are molded of durometer material equal or harder than the cathetertube body which have precisely molded tapered configurations and theopenings in which have smoothly chamfered edges which are'not enlargedas in prior art tips.

Still further and other objects of this invention will become evidentfrom a review of the detailed description which follows.

FIGURES and shows in detail the mounting features of both the cuff andthe tip.

FIG. 4 shows partly in perspective and partly in section constructionaldetails of one embodiment of the special tip of this invention.

FIG. 5 shows partial closure of the tip of a prior art catheter whereinthe body of the catheter and tip are made of a single material ofrelatively low durometer.

FIG. 6 is a section view ofa retrofit cuff assembly and separateinflation lumen in accordance with this invention.

FIG. 7 shows several aspects of the retrofit silicone rubber cuff ofFIG. 6 in use upon a catheter body of dissimilar material. This figurealso shows the free shape of the cuff, the shape upon initial contact,upon initial full seal, and the shape upon overinflation.

FIG. 8 shows in sectionthree embodiments of the marginal seal of aretrofit balloon on a catheter body of dissimilar material.

FIG. 9 shows in section three embodiments of a retrofit cuff whichprovides for smooth, non-irritating edge seal of the cuff to dissimilarcatheter body materials.

FIG. 10 shows in section two other embodiments of the cuff constructionof this invention.

FIG. 11 shows in plan view the generally hyperbolic shape of thecatheter tube of this invention as compared to the generallysemicircular shape of prior catheters.

FIG. 12 shows in section another embodiment of the tip of this inventionand a method of securing the tip to a catheter tube body.

DETAILED DESCRIPTION The following detailed description makes particularreference to a polyvinylchloride or stainless steel catheter tube. Thisdescription is by way of example only and is not meant as limiting ofthe invention since the principles shown herein may be applicable tocatheter tubes of various materials. The selected durometer tips asdescribed in this invention are described as constructed ofpolyvinylchloride by way of example only. It should be understood thatthey may be made of any plastic or elastomeric material which permitsthem to be bonded to the main body of the catheter tube as by chemicalbonding, solvent bonding, thermal treatment, or mechanical interlock. Itshould also be understood that while the description is made herein withreference to an endotracheal tube, this description is by way of exampleonly and the principles of this invention may be applied to all types ofcatheter tubes, including tracheostomy tubes, Foley catheters,endotracheal tubes, urethral catheters, and catheters for use ingastric, esophageal, pharyngeal, nasal, intestinal, rectalcolonic,choledochal, arterial, venous, cardiac and endobronchial applications.

FIG. 1 shows, by way of example an endotracheal or tracheostomy tube 1which is composed of main body portion 2, broken into several parts soas to show within the space available the proximal end assembly 3,distal end assembly 4, and inflation assembly 5. The proximal assembly 3may include a connection 6 for attachment to a source of oxygen orvaporous anesthetic for administration to the patient by way of thelungs. This connector 6 may be inserted into the proximal end 7 of themain body portion 2, which end is terminated normal to the long axis ofthe tube. The inflation assembly 5 includes a pilot tube 8 connectingmedially of the main portion 2 with an inflation lumen 9 which is formedin the wall of the main body portion. The proximal end of the pilot tube8 is terminated in an appropriate connector 10 for attachment of a cuffinflating device. such as a syringe for inflating the cuff with air orfluid, such as water or saline solution. As discussed herein, theinflation medium for the cndotracheal tubes is air. administered by wayof hypodermic syringe (not shown) attached to the connector 10. Also byway of example. the description herein is of a main body portion 2extruded from polyvinylchloride plastic of a durometer suitable forflexibility in use in medical situations, yet not so soft and flexiblethat the tube collapses in use. For example the durometer of the PVCtube typically ranges from 60-85 Shore A hardness. The inflation lumen 9is normally formed during the extrusion operation.

It should be understood, however, that the inflation lumen 9 may bedisposed in any manner desired in association with the main body portion2. For example, the inflation lumen need not be in the wall 11 of thebody 2, but may be formed by attaching the pilot tube 8 to the bodyportion 2 along the side, extending in the direction of the proximal anduntil it connects to the cuff assembly. Likewise, as shown in FIGS. 6and 7, the pilot tube 8 with inflation lumen 9 may be contiguous to thetube 2 but not connected thereto.

The cuff assembly 12 is placed medially of the distal end of the mainbody portion 2 and the interior of the cuff communicates with theinflation lumen 9 by means of one or more apertures 13, 13. FIG. 1 alsoshows one embodiment of the frictional securing means for the siliconerubber cuff comprising a pair of high durometer and modulus sealingrings 14, 15. The outer cuff member 16 is the low durometer and modulussilicone rubber member (Shore A hardness less than about 30) whichcontacts tissue, such as the tracheal wall, and has special properties(as described in more detail below) which tend to lessen inducing tissuepressure necrosis by vascular flow cutoff in tissues adjacent to areasof contact of the inflated cuff. The outer silicone rubber cuff memberis chemically bonded to the securing inner member or members by the useof an adhesive silicone rubber which may be air-dried and/or heat-curedto provide bonds 17, 17' (see FIG. 3) which are permanent underconditions of use. For example, a Dow- Corning Silastid brand medicalgrade type A adhesive may be used, or any suitable RTV type may be used.

The distal end assembly 4 includes a precision molded tip 19 secured tothe distal end 18 of the body 2 (see FIG. 3). The tip may be seen inmore detail in FIGS. 3, 4 and 7. With reference to FIG. 4, the tip 19 isprecision molded of a plastic or elastomeric material of equal or harderdurometer than the main body portion 2. Whereas the typical durometer ofpolyvinylchloride body portion tubes ranges from a Shore A hardness ofabove 60 to about 85 the durometer of tip 19 will range from 60-95. Weprefer the tip durometer to be greater than the body durometer, in therange of from about 75 to about 95. While the tip is shown and describedherein by way of example as constructed of polyvinylchloride, it shouldbe understood that the tip may be of any moldable plastic or elastomericmaterial which can be secured to the body portion 2 as by adhesive,solvent bonding, thermal bonding, (such as infrared. resistance heating.RF. and including spin welding). or frictional and mechanical interlockwith the body portion 2. We prefer bonding oftip 19 to the distal end 18of body 2 by means of compatible adhesives, solvents or plasticizers.

The tip 19 may include a proximal flange portion 20 which may be taperedinwardly from approximately the region of the shoulder 21 to theproximal edge 22. The proximal edge 22 is typically normal to the axisof the tip and body portion 2. The distal portion 23 has an inwardlytapered profile and terminates in a transverse leading edge 25, in thecase of cndotracheal or tracheostomy tubes. The transverse leading edge25 has both an outer chamfer or rounded edge 26 and an inner chamfer orrounded edge 27. The axial bore 28 of the tip 19 has an inner diameterthe same as the inner diameter 29 of the body portion 2 (see FIG. 3).The precision molded leading edge and tapered profile provides for easeof insertion and withdrawal of the catheter tube from the body while therelatively long. in the axial direction, flange portion 29 provides foradequate mechanical or chemical seal to the body portion 2.

The chamfered leading edge is precision molded thus providing cathetertubes having identical insertion tips. The leading edges of the tubes ofthis invention are not irregular in shape, rough or sharp due to atransverse cut, nor are they larger on the outside than the main bodyportion, while at the same time smaller at the inner diameter, due tobeading from flame or other thermal smoothing of the transverse cutedge. In addition, the increased hardness (durometer) prevents foldingover of the tip upon striking an obstruction when inserted into thebody, as seen for example in FIG. 5. Prior PVC tips have a transverselycut end 31, and trailing edge 32 of which may be relatively sharp, whilethe leading edge typically illustrates the beading 33, and folding asshown at 34 in FIG. 5.

It should be understood that while the tip flange portion 20 may have aninward taper such that the proximal edge 22 has a wall thickness thinnerthan the distal portion of flange 20, the flange may be of equalthickness throughout as shown by uniform wall thickness 36 in FIG. 7.This wall thickness may be varied to providefor smooth transitionbetween the tip and the body portion 2 or the cuff assembly 12. As shownin FIG. 1, there may be a gap 37 between the proximal edge of the tip 19and the distal end of the cuff assembly 12. As seen in FIGS. 3 and 7,the flange portion 20 may extend proximally far enough to abut the cuffassembly 12. Where the cuff assembly 12 is spaced from the proximal edge22 of the tip flange portion to leave a gap 37 (see FIG. 8), that gapoptionally may be filled with a material to provide a smooth transitiontherebetween. For example, a silicone rubber adhesive material 38 may beapplied at this juncture to provide a smooth transition. Although thesilicone rubber adhesive may not bond to the polyvinylchloride tip or tothe polyvinylchloride or metal body portion 2, it will bond to thesilicone rubber cuff members and provide a smooth transition.

FIG. 12 illustrates another embodiment of the tapered tip 19. In thisembodiment, flange 20 is replaced by proximally extending bevel 71. Tosecure this tip form to tube body portion 2, tip 19 is slipped overmandrel 69 which is then fitted into bore 29 of tube 2. The mandrel maybe spring biased axially in the medial direction of tube 2, as shown bythe arrow on the right of FIG. 12. Heat is applied eircumferentiallyfrom source 70, 70 to the bevel and distal end 18 of the tube 2. Uponsoftening sufficient to weld the tube to the tip. the biasing forcepresses the parts together to make a secure joint. The mandrel issufficiently tight fitting that there is substantially no flashing ornarrowing of the bore at the joint. Alternately. the bevel may be tilledwith glue or adhesive, as at 72 in FIG. 12.

Whether collar or bevel type preformed tips are used. the assembly timeis on the order of 3-5 seconds. as compared to 8-15 seconds for cuttingand tip heatsmoothingoperations of the prior art. The same principlesapply to tips for other types of catheters, such as eyelet type tips forFoley-type catheters.

In addition to the medically smooth insertion tip providing for atransition between the transversely leading edge and the main bodyportion of the catheter, we may provide the main body portion with anappropriate preformed curve, as seen in FIG. 11. As shown by the dottedcurve 39, prior tubes had a set which was a portion ofa semicircular arcof radius about 12-1 8 inches. In contrast. we provide a preformed curveor set to the main body portion which is generally hyperbolic for thistype of tube. This more nearly conforms to the general shape of thetrachea while the patient is in the supine position in surgery. Thehyperbolic curve is preformed in the polyvinylchloride tube by warmingthe tube, placing it in the appropriate hyperbolic form and letting itcool until the curve is set in the plastic. Because of the circularcurve of prior tubes they exhibit drag of the tip along the tracheaduring insertion. or upon retraction of the insertion obdurator. Afterobdurator retraction, the tips may rest against the trachea wall causingsevere necrosis. See McGinnis et al., An Engineering Analysis ofIntratracheal Tube Cuffs, Anaesthesia & Analgesia, Current Researches,50, 557-64 I97l The hyperbolic curve 40 of our tubes is set into thetube such that the short radius" portion of the curve 42 is near theproximal end while the relatively straight portion of the curve 41 is atthe distal end. With the precision molded tip 19 of this invention, thetube terminates in an axially straight portion which minimizes side walldrag during insertion and tip necro- SIS.

FIG. 3 also shows in more detail one embodiment of the inflation cuffand in accordance with this invention. The cuff assembly 12 basicallycomprises two elements, a sealing element and an outer cuff member whichexpands upon inflation to provide the desired seal. As shown in FIGS.6-9, the inner seal member 43 comprises a cylindrical tube extendingaxially substantially the length of the outer cuff member 16. However,as shown in FIGS. l-3, the inner seal member 43 may also be composed oftwo seal rings 14 and 15 rather than an inner continuous cylindricaltube. In both embodiments, the scaling function is essentially similar.Either rings 14 and 15, or the inner seal 43 grippingly engage the tubebody 2 securing the cuff member 12 thereto and preventing leakage ofinflation fluid from either the proximal or distal margins of the cuffassembly 12. The seal member has a compression factor of from 5-50percent, that is, the relaxed ID. of the seal member is 5-50 percentless than the CD. of the catheter tube on which it is fit, depending ondurometer, such that the harder the durometer of the tube the greaterthe compression factor. We prefer compression factors in the range offrom 10-30 percent for normal durometer range of PVC tubes.

Turning first to the embodiment of the cuff assembly shown in FIGS. 1-3,the inner seal member of this em bodiment includes a plurality of rings14 and 15 one of each being disposed adjacent the proximal and distalends of the cuff assembly, respectively. In both embodiments, the innerseal members are constructed of a silicone rubber of higher modulus anddurometer than the cuff. and which has a compression factor of 5-50percent in proportion to the tube durometer. The outer. extensible cuffmember 16 is bonded to the inner seal member tube 43 or rings 14, 15 bymeans of an appropriate adhesive or curable silicone rubber material.Since both members, cuff and seal, are silicone rubber, they can bebonded by conventional techniques. The rings or tubular inner sealmember is then expanded mechanically and placed over the tube, or thetube inserted through the expanded seal member. The mechanical expansionis then released and the rings or sleeve firmly grips the outsidesurface of the body member. In the case of polyvinylchloride, anexcellent frictional fit is provided due to its slightly tacky surfacecharacteristics. Since these bands do not come into contact with thetissue walls, they may be of properties which lend themselves togripping the tube and provide for integrity of inflation fluid seal.

As seen in FIG. 3, the rings 14 and 15 may extend beyond the ends of theouter cuff member 16 to provide for a step-wise transition between theouter surface 44 and the outer surface of the cuff 16. In thealternative, the ring 14 may be placed inwardly of the end of the outercuff member 16 so that a margin 45 of the outer cuff member overlaps toprovide for a tapered, smooth transition. As shown in FIG. 3, the margin45 may be extended axially sufficiently far to abut the proximal edge 22of the tip assembly 19.

FIGS. 6-9 illustrate another embodiment of the invention in which theinner seal member is tubular in configuration. FIG. 6 shows a retrofitassembly comprising the inner sleeve seal member 43, which is secured tothe outer extensible cuff member 16 along margins adjacent the proximalend 46 and the distal end 47 thereof by means of a suitable adhesive 17,17. This provides for inflation space 48 which may be inflated by meansof the pilot tube 8 and inflation lumen 9 connected to appropriateinflation means such as a syringe (not shown). Like the ring form ofsealing member, the inner seal sleeve member 43 has a compression factorof 5-50 percent, with the inner diameter 49 of the seal being smallerthan that of the tube. The sealing sleeve member 43 securely grips theouter surface of the tube 2 providing for a full seal. This is moreparticularly illustrated in the lower portion of FIG. 7 which shows thecuff in its freely inflated shape. The arrows also show a hydrostaticassist effect wherein the inflation fluid serves both to expand theouter cuff member 16, while at the same time pressing inwardly on thesealing sleeve member 43, thereby increasing the seal of the cuff to thetube body.

The inner seal sleeve member 43 and rings 14, 15 are typicallyconstructed of a high modulus silicone rubber which may be molded orextruded having a durometer, expressed as a Short A hardness, in therange of 40-90 typically 60-80. While the seal member material may bemolded or extruded, we prefer to extrude the seal members and heat curethem. One manner of placing the sealing member sleeves or rings over thetube is by slipping them over the tapered tip assembly 19 and onto thetube body portion. Since the tip is tapered, it facilitates theinsertion of the tube 1 into the reduced diameter sleeve or rings.

The upper portion of FIG. 7 illustrates the high degree of trueconformability of the outer cuff member 16 when in contact with tissue,such as trachea wall 50. As the cuff is inflated, the outer cuff member16 expands outwardly until it touches the trachea wall. Characteristicof our outer cuff materials is the fact that this first contact occursat relatively low pressure and low volume. The pressure at first contactmay be measured and identified as P('. Since the trachea is not round,but rather is generally triangular with the apices of the trianglehaving rounded corners of short radius, the initial contact along thewalls leaves gaps at these apices. Continued inflation, however, pressesour outer cuff member into contact and complete conformity with all thewalls of the trachea. The pressure at this initial full seal may also bemeasured, and it is identified as P The longitudinal (axial) shape ofthe cuff of this invention may be seen in FIG. 7 at both initial contactthe P shape shown on the right hand side of FIG. 7, and at initial fullseal, the P shape identified in dotted lines at the left side of FIG. 7.

Our cuff material is constructed of a low modulus silicone rubbermaterial of relatively low durometer, high elongation, low strength, andlow stress upon sealing, which values may be selected to provide a cuffwhich, at initial substantially full seal, provides a transmuralpressure P defined as the seal pressure minus the contact pressure (P,-P of values below those which tend to induce vascular cutoff pressureswhich produce medically significant tissue pressure necrosis. Normally,this would be below about 30 mm. Hg. pressure transmitted to capillarybeds, or the equivalent value of about lO-l mm. Hg. transmitted to theefferent venous system adjacent the cuff-tissue contact area. We preferthat this transmitted pressure be below about 2025 mm. Hg. relative tothe capillary bed site or about 10 mm. mercury compressive pressuretransmitted at the efferent venous site.

A typical composition suitable for cuffs having below the above criticaltransmural pressure values is one which is of a low modulus, moldedsilicone rubber having a Short A hardness of less than about 30, anelongation of greater than about 1000 percent, a tensile strength ofbelow about 700 psi, and a stress value upon sealing inflation of lessthan about 30 percent of the breaking stress of the cuff material. Othercompositions producing the below critical pressure values may also beemployed.

The importance of being below the critical value can also be seen fromthe left hand side of FIG. 7. Since the anesthetist in actual practiceis not able to precisely gauge in each instance the exact moment ofinitial full seal, he is apt to overinflate the cuff to ensure that aseal is made. This is particularly true of prior art catheters employingoversize, large residual volume, cuffs. Since in order to havevisibility upon insertion of oversize-cuff-type tubes, the anesthetistselects undersized catheter tube bodies, i.e., those with a small outerdiameter. But with small O.D. tubes, the overinflation reaches orexceeds the elastic limits of the PVC or latex outer cuff prior to fullseal, and over-critical pressures are generated. In contrast, oursilicone rubber outer cuff member conforms generally to the outer shapeof the tube i.e. is not oversized, thus permitting insertion visibility.At the same time our cuffs are low volume, low pressure, and highlyconformable due to their low modulus and hardness, and highextensibility. Thus the anesthetist may select one of our cathetershaving an outer diameter more nearly approximating the size of thetrachea. This provides for maximum air inflow through the lumen of theendotracheal tube and full seal at extremely low volumes. Since thetransmural pressure generated by the cuffs of our invention at full sealare generally below critical, the anesthetist has ample margin for errorto over-inflate the cuff without generating over-critical pressures. Forexample, actual measurements have shown that the anesthetist may have upto about 55 percent leeway to overshoot initial sea] as to pressureand/or volume injected into the cuff. In addition, the highconformability and extremely elastic nature of our silicone rubbercauses the cuff to extend laterally, rather than radially outwardly,upon over-inflation. This illustrated by the over-inflated shape in theupper left in FIG. 7. In descriptive parlance, the cuffhotdogs laterally(axially), rather than ballooning, i.e. expanding only radially as inthe case of prior art PVC or latex cuffs. The cuff of our inventionconforms to the trachea shape, rather than forcing the trachea to itsshape. 7

FIG. 6 shows the inner seal member 43 terminating at either end 46, 47co-extensively with the proximal and distal ends of the outer cuffmember 16. In another embodiment shown in FIG. 7, axial margins ofeither cuff member 16 or inner seal sleeve member 43 may extend beyondthe other to provide for more smooth transition between the outersurface of the tube body 2 and the outer cuff member 16. For example, inthe upper half of FIG. 7, the outer cuff member 16 has a proximal margin51, a distal margin 52 each of which extends beyond the ends 46, 47respectively, of the seal sleeve member 43. The distal margin 52 isshown as abutting the proximal edge 22 of the precision molded tip 19.This provides for an extremely smooth transition between the tip and theouter cuff member 16.

The lower portion of FIG. 7 shows a step-wise transition with proximalmargin 53 and distal margin 54 of the inner seal sleeve member 43extending beyond the ends of the outer cuff member 16.

FIG. 8 shows still another embodiment of the retrofit assembly shown inFIG. 6. In this embodiment, the pilot tube 8 may be omitted and aperture55 provided in the seal sleeve member 43 for communication withinflation lumen 9 provided in the wall ofa stainless steel tracheotomytube 56. The upper left portion of FIG. 8 shows a step-wise transitionwith the proximal margin of the sleeve member 43 extending beyond theouter cuff member 16. In contrast, the upper right hand portion of FIG.8 shows the reverse overlap with distal margin 52 of the outer cuffmember 16 overlapping the seal sleeve member 43. The lower half of FIG.8 shows the gap 37 between the proximal edge of the tip 19 being filledwith a silicone rubber adhesive material 38.

FIG. 9 illustrates still further embodiments of the invention withprovisions for providing a smooth transition between the cuff and thetube body. In FIG. 9 various types of grooves and overlaps of the cuffand sleeve members are shown. The upper left hand portion of FIG. 9shows a generally U-shaped groove 57 molded or incised into the body ofthe plastic, elastomeric or metal tube 56. In this embodiment, theproximal margin 51 of the outer cuff 26 overlaps slightly the sealingsleeve member 43. A smooth transition is provided as shown. At the upperright of FIG. 9, an oblique V- shaped groove 58 is molded or incisedinto the tube body wall, and co-extensively terminating outer cuffmember and sealing members fit snugly therein to provide a smoothtransition. The lower portion of FIG. 9 shows on the left hand end thereverse overlap in a U- shaped groove, and the right hand end showscoincident termination of both the outer cuff member and the sleevemember in a U-shaped groove.

FIG. 10 shows still another embodiment of the cuff of this inventionwherein the sealing rings 14, have been molded integrally or cured withthe outer cuff member 16, placed medially thereof, and the outersurfaces of which are tapered to provide for smooth transition. Theouter cuff member 16 is molded or cured to a proximal thickened marginportion 59 and a distal thickened margin portion 60 which have theproperties attributed to the securing rings 14 and 15, respectively. Asshown in the upper half of FIG. 10 these thickened portions may be insetinto one or more grooves 61, 62 and 63 incised or molded into the bodyof the tube. At the upper left hand portion of FIG. 10, there can beseen a plurality of inwardly projecting feet 64 and 65 which mate withthe grooves 63 and 62 respectively. A larger, single foot 66 is shown ingroove 61 in the upper right hand portion of FIG. 10. The outer edges ofthe thickened margin portions 67 and 68 are chamfered to provide forsmooth transition between the outer surface of the tube body and theouter cuff member 16. The lower half of FIG. 10 shows this type of cuffplaced on a standard tube, the outer surface of which has no specialgrooves.

Several other advantages to the precision molded tip of this inventionare important. First, it is possible to provide the tip withradio-opaque properties such that it may be seen by x-ray orfluoroscope. For example, the PVC composition may be compounded with abarium sulfate filler material. This permits the very tip of thecatheter to be located when the tube is in place in the body. Inaddition, the thermoplastic polyvinylchloride material, after injectioninto the precision mold, may be cooled rapidly by running cooling waterthrough the walls of the steel mold. The rapid cooling promotes a veryfine surface crystallization which gives the tip a frosted appearance.This frosted appearance is actually a microscopic surface texturing orslight deformation". This surface texturing is extremely helpful in theinsertion of the tube into the body since it promotes ease of slidingdue to a mechanical wettability effect. Normally, polyvinylchloride ofmoderate durometer is relatively tacky to the touch, and it is difficultto insert a suction or other type of tube of similar material throughthe center lumen of the trachea tube. In order to permit the tubes toslide one against the other, the surface of one or both should bemicroscopically roughened. Similarly, the outer surface of the tube isadvantageously roughened. This is particularly critical of the tube tipsince it meets initial resistance upon insertion. By the frosting effectachieved by mold temperature control, we are able to promote ease ofinsertion. Likewise. this frosted effect can be produced by slightchemical etching or mechanical abrading of the mold surface. The tipsmay also be color coded for size or type by use of conventional dyes forease of selection and prevention of error in use. For example, adifferent color may be used to identify each of the 12 sizes of trachealtubes ranging from 5 to 12 mm. [.D.

It should be understood that various modifications within the scope ofthis invention can be made by one of ordinary skill in the art withoutdeparting from the spirit thereof. We therefore wish our invention to bedefined by the scope of the appended claims as broadly as the prior artwill permit, and in view of this specification if need be.

We claim:

1. An improved tracheal tube comprising:

a. a flexible, tubular body portion with a durometer of above 60 toabout 85 having a central passage extending axially therein from aproximal to a distal end;

b. an inflatable cuff positioned on the tubular body portion;

c. means for inflating said cuff;

d. a separate molded tip secured to the distal end of the flexibletubular body portion,

i. said tip having a distal portion and having an aperture thereincommunicating with the central passage of said tube body portion,

ii. said tip being resilient material having a durometer higher than thedurometer of said flexible tube body portion, and in the range of fromabout to about 95,

iii. said distal portion having a distally extending inward taper and achamfered leading edge of uniform thickness around its entirecircumference oriented transverse to the axis of the aperture for easeof insertion into a body, and

iv. said tip also having a proximal portion with an inwardly bevelededge abutting and heat sealed to the distal end of said tube bodyportion,

v. said heat seal providing a smooth transition between the tubular bodyportion and the tip on both the exterior and the interior thereof;

e. said tip providing a tracheal tube wherein the tip does not fold overupon striking an obstruction when inserted into the body.

2. A tracheal tube as in claim 1 wherein said tip is color coded toidentify the inner diameter of the tube body central passage for ease ofrecognition and size selection for surgical use.

3. A tracheal tube as in claim 1 wherein said tip material isradio-opaque to render the position of said tip 10- catable when in use.

4. A tracheal tube as in claim 1 wherein said tube body and said tipassembly are polyvinyl chloride plastic-containing materials.

1. An improved tracheal tube comprising: a. a flexible, tubular bodyportion with a durometer of above 60 to about 85 having a centralpassage extending axially therein from a proximal to a distal end; b. aninflatable cuff positioned on the tubular body portion; c. means forinflating said cuff; d. a separate molded tip secured to the distal endof the flexible tubular body portion, i. said tip having a distalportion and having an aperture therein communicating with the centralpassage of said tube body portion, ii. said tip being resilient materialhaving a durometer higher than the durometer of said flexible tube bodyportion, and in the range of from about 75 to about 95, iii. said distalportion having a distally extending inward taper and a chamfered leadingedge of uniform thickness around its entire circumference orientedtransverse to the axis of the aperture for ease of insertion into abody, and iv. said tip also having a proximal portion with an inwardlybeveled edge abutting and heat sealed to the distal end of said tubebody portion, v. said heat seal providing a smooth transition betweenthe tubular body portion and the tip on both the exterior and theinterior thereof; e. said tip providing a tracheal tube wherein the tipdoes not fold over upon striking an obstruction when inserted into thebody.
 2. A tracheal tube as in claim 1 wherein said tip is color codedto identify the inner diameter of the tube body central passage for easeof recognition and size selection for surgical use.
 3. A tracheal tubeas in claim 1 wherein said tip material is radio-opaque to render theposition of said tip locatable when in use.
 4. A tracheal tube as inclaim 1 wherein said tube body and said tip assembly are polyvinylchloride plastic-containing materials.